A wheel loader is a vehicle for mainly executing an excavation work and includes a vehicle body frame, a working unit, front and rear tires, a cab and etc. Further, the vehicle body frame includes a front frame, a rear frame and a coupling part. The front frame is coupled to the rear frame through the coupling part, while being allowed to turn in the right-and-left direction.
Such wheel loader includes a hydraulic transmission for executing switching between forward travelling and rearward travelling and gear shifting. Further, the transmission is provided with rotary shafts such as an input shaft, an intermediate shaft and an output shaft, hydraulic clutch devices attached to these shafts, gears, a parking brake and etc.
Thus, a friction part including a clutch device and a brake device, a slide part such as a bearing, and an engaged part using a spline are disposed inside the transmission. Therefore, it is required to supply lubricating oil to these components.
In view of this, a hydraulic system as described in Japan Laid-open Patent Application Publication No. JP-A-2010-174971 and a structure as described in Japan Laid-open Patent Application Publication No. JP-A-2001-227563 have been provided.
The hydraulic system described in Japan Laid-open Patent Application Publication No. JP-A-2010-174971 is provided with a transmission lubricating circuit branched from a high pressure circuit for supplying an operating oil to a clutch, and is further provided with a transmission lubrication backup circuit branched from a steering lubricating circuit. The transmission lubrication backup circuit is connected to the transmission lubricating circuit. Further, the oil used for lubrication by these circuits is accumulated in a transmission case and is then returned to a steering device.
On the other hand, the transmission described in Japan Laid-open Patent Application Publication No. JP-A-2001-227563 is configured to forcibly lubricate the clutch by means of a drain oil of a power steering mechanism in order to implement clutch lubrication at a low cost.
Further, Japan Laid-open Patent Application Publication No. JP-A-H06-249324 describes arrangement of a tub located above an automatic gear shifting device as a fueling device of the automatic gear shifting device in order to collect the lubricating oil upwardly stirred by gears within the transmission. The lubricating oil, collected by the tub, is then configured to be supplied to respective slide parts by the action of gravity.